Cardiovascular-related antinociception (mediated by endogenous opioids) is an important component of adaptation to acute pain in healthy individuals. Previous research indicates possible deficits in endogenous opioid levels in chronic pain patients, although little is known about the functional effects of these deficits. This study will: 1) examine the relationship between resting blood pressure (BP), acute pain sensitivity, and clinical pain in chronic pain patients, and 2) examine differences in degree of endogenous opioid mediation of this BP/pain relationship between pain patients and normals. Thirty chronic pain patients and 30 healthy normals will undergo a laboratory ischemic pain stimulus once under placebo and once under opioid blockade with naloxone (randomized, counter-balanced order). In both sessions, BP will be determined at resting baseline, and periodically throughout the protocol. Pain patients will also rate their clinical pain before and after drug administration. As in previous work, it is expected that normal patients will display a significant positive correlation between resting BP and acute pain sensitivity, which will be at lease partially eliminated by naloxone. Pain patients are expected to demonstrate little correlation or a positive correlation between resting BP, and both clinical pain and acute pain sensitivity, and will be unresponsive to opioid blockade.